Elena, her father Dr. Arboria and the guy in the straight jacket appear to be the only patients left. Apart from Dr. Nyle, Margot and the Sentionaut(s), there are no other staff that we see. By the end of the film, the remainder of the staff are dead except for the Sentionaut(s). There are already signs that equipment at the Institute are just beginning to fail (the malfunctioning drawer button that revealed Nyle's notebook for instance).
The film ends just as Elena has come upon a nearby neighborhood. No doubt, she is going to knock on someone's door and whoever answers is (hopefully) going to help her. It's likely that someone is going to call the police who will question her.
Eventually the police are going to search the nearby area, find the bodies, find Barry's car, run the plates, search his house and find Rosemary's body. At that point, they'll try to get in touch with his workplace but get no answer.By then, they would have all the probable cause they need to get a warrant to search the Institute and find even more bodies and god-knows what else.
